How to check if string contains Latin characters only?

Question

How to check if a string contains [a-zA-Z] characters only?

Example:

var str = \'123z56\';

Answer 1

All these answers are correct, but I had to also check if the string contains other characters and Hebrew letters so I simply used:

if (!str.match(/^[\d]+$/)) {
    //contains other characters as well
}